1. Field of the Invention
The present invention relates to an endosteal root-form dental implant system. More specifically, this invention relates to a self-drilling endosteal hollow-basket implant system with a tissue extension (sometimes referred to as a transmucosal abutment member) that supports and holds a keeper with shock-absorbing resilient means. Inserted onto the keeper may be various dental prosthesis designs.
2. Brief Description of the Prior
It is beyond the scope of this brief description to review the early attempts of men to replace missing teeth. Studies of Egyptian mummies from the middle kingdom up to Ptolomy's time revealed different processes of implantation.
A scientific breakthrough in the area of dental implants was achieved by Swedish Professor Per-Ingvar Branemark and co-workers. Combining a two-stage surgical technique with the use of titanium fixtures, these scientists achieved predictable results in surgical placement of permanent dental implants. Their continued studies in the early 1960's provided the basis of modern implantology.
However, because of the lack of periodontal ligaments between the bone and the titanium fixture, the implant lacked the natural motion and shock-absorbing capability of natural teeth.
Screw attachments have been employed between bone and fixture but under great stress they tend to fracture. In a publication titled "Dental Implant Prosthodontics" (J. B. Lippincott Company 1991 ISBN 0-397-51045-4), Ronald P. Desjardeins observed "The most common prosthesis problem that the author has thus far noted is the loosening or breakage of the gold locking screw with the resultant loosening of the prosthesis."
In the early 1970's, Dr. Kirsch from Germany designed an implant system called IMZ with a plastic shock-absorber called the IME. This device provides similar elastic properties as a periodontal ligament. The IME, which is a threaded intermediary sleeve, is installed inside of the implant by screwing it into the threaded bore of the implant. The sleeve has a threaded bore, into which a prosthesis is screwed.
However, in the same publication mentioned above, Robert J. Chapman observed that "the IME must be replaced every year or two, because it is plastic and will deteriorate somewhat with function."
That deterioration of the plastic sleeve opens a way for bacteria and changes the mechanical characteristics of this device. U.S. Pat. No. 4,622,010 describes a similar device that avoids the threads on the plastic sleeve.
U.S. Pat. No. 4,993,950 describes a keeper system which uses an O-ring "to permit universal `rocking` motion of the keeper member relative to the true transmucosal cuff."
U.S. Pat. No. 5,006,068 describes a dental implant system with resilient force dampening means on the prothesis itself.
These designs provide a single means of shock-absorbing capacity and do not imitate the longitudinal movement of natural teeth. Other implant systems fail to mirror the movement of natural teeth. Such systems may feel unnatural to the person using such prior art dental implant systems. Furthermore, when a prosthesis is cemented to a natural tooth abutment and an implant abutment, the cement will be placed under great torquing stress to both ends of the prosthesis. This torquing stress may break the cement and cause the failure of the prosthesis.
Hollow-basket implants have advantages over the cylinder type. First, they require a minimum of bone removal that results in a less traumatic osteotomy. Second, they provide maximum anchoring surface and adequate mechanical strength. Because of its tubular shape with various perforations, it is able to withstand tension, compression or shearing stress and torque. The hollow-basket design also allows a two-sided growing of the bone tissue through the vents of the implant. Examples of prior art efforts are shown in one or more of the following U.S. Patents: U.S. Pat. No. 4,431,416; U.S. Pat. No. 4,951,819; U.S. Pat. No. 4,960,381; U.S. Pat. No. 4,842,517; U.S. Pat. No. 4,379,694; U.S. Pat. No. 4,657,510.
However, these prior art hollow-basket implants are not self-drilling. The insertion of prior art dental implant system involves a two-step surgical procedure. This is typical of endosteal root-form implant and is well known in the previous art. For the purpose of illustration, however, we are going to summarize the events of the two steps. First, the surgeon cuts a flap on the mucosa and drills a socket on the bone where the implant is then placed with a cover screw. The soft tissue is repositioned and the implant site is closed to avoid any movement of the implant and to prevent infection. Later in the second step, after osseointegration is complete, the surgeon uncovers and removes the cover screw. The surgeon then installs a healing cap which is later replaced by a tissue extension. It is into the tissue extension that the restoration is installed. On occasion the restoration is attached to an intermediate device, located between the tissue extension and the restoration, which we have referred to as a keeper.